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Chiral plasmonic nanostructures attracts attention because they are potentially applicable to optical materials such as enantioselective sensors and metamaterials, as well as photoelectrochemical devices. Chiral nanostructures are often prepared by electron beam lithography or synthesis based on DNA templates. We have recently developed a photoelectrochemical method, in which handedness of the chiral nanostructure can be controlled by right- or left- circularly polarized light. The photoelectrochemical method is based on plasmon-induced charge separation (PICS),1,2 in which electrons are injected from a plasmonic metal nanoparticle to a semiconductor such as titania in direct contact. In PICS, anodic reactions often occur at the resonance sites of the plasmonic nanoparticle, at which electron oscillation is localized.3,4 Energetic electron-hole pairs generate at the resonance site, and holes are used for the local anodic reaction, probably via trap sites. On the basis of the mechanisms, we have demonstrated site-selective etching of silver nanoparticles and site-selective deposition of lead oxide on gold nanoparticles. Under right-circularly polarized light (CPL), distribution of the resonance sites could be the mirror image of that under left-CPL.5 Therefore, we performed site-selective deposition of lead oxide on gold nanocuboids on titania under right- or left-CPL.6 As a result, lead oxide was deposited on the gold nanocuboids in a chiral geometry. The nanostructures thus obtained exhibited circular dichroism (CD), and the CD spectrum obtained for the structure prepared under right-CPL was opposite to that obtained for the structure prepared under left-CPL. Reversible switching of the handedness of the chiral plasmonic nanostructures can also be possible.7 This method also allows us to fabricate spiral nanostructures. 1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005). 2. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review]. 3. I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012). 4. T. Tatsuma and H. Nishi, Nanoscale Horiz., 5, 597 (2020) [review]. 5. S. Hashiyada, T. Narushima, and H. Okamoto, J. Phys. Chem. C, 118, 22229 (2014). 6. K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018). 7. K. Morisawa, T. Ishida, and T. Tatsuma, ACS Nano, 14, 3603 (2020).

Plasmon-induced charge separation (PICS)1,2 involves electron transfer from plasmonic noble metal nanoparticles or compound nanoparticles to an n-type semiconductor such as TiO2. Oxidation reactions involved in PICS are based on a charge accumulation mechanism (Figure a) or a hole ejection mechanism (Figure b).3 The latter enables nanoscale local oxidation at relatively positive potentials.4-7 This can be applied to photoinduced nanofabrication beyond the diffraction limit of light. For instance, chiral plasmonic nanostructures can be prepared by PICS under right or left circularly polarized light (Figure c).8,9 Some other applications of the plasmonic hole ejection will also be mentioned. Enhancement of PICS with hole ejection through plasmon coupling10 and its application to photocatalysis will also be described. References Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005). T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review]. T. Tatsuma and H. Nishi, Nanoscale Horiz., 5, 597-606 (2020) [review]. E. Kazuma, N. Sakai, and T. Tatsuma, Chem. Commun., 47, 5777 (2011). I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012). K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016). H. Nishi, M. Sakamoto, and T. Tatsuma, Chem. Commun., 54, 11741 (2018). K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018). K. Morisawa, T. Ishida, and T. Tatsuma, ACS Nano, 14, 3603 (2020). T. Ishida and T. Tatsuma, J. Phys. Chem. C, 122, 26153 (2018). Figure 1

Plasmon-induced charge separation (PICS)1-3 involves electron transfer from plasmonic nanoparticles of Au, Ag, or Cu to a semiconductor, typically TiO2.1-4 The electron transfer is caused by external photoelectric effects (including hot carrier injection) or interfacial electron transition.3 We have reported that oxidation of Ag to Ag+ occurs at the Ag nanoparticle surface in PICS of Ag-TiO2 systems,5 and this reaction occurs preferentially at the sites where optical near field is localized.6-8 This can be explained in terms of ejection of energetic holes from the nanoparticles as Ag+ ions.8,9 This possibility has been further investigated on the basis of other anodic reactions. For a system with isolated Au nanoparticles on TiO2, the interface mode may be more important than the full-surface mode. However, plasmon coupling between two nanoparticles, which enhances full-surface mode but not necessarily enhances the interface mode, increases the PICS efficiency. This could also indicate that not only injection of electrons from Au nanoparticles into TiO2 but also ejection of holes from Au nanoparticles play an important role in those PICS systems. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005). Y. Tian and T. Tatsuma, Chem. Commun., 2004, 1810. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review]. E. Kazuma and T. Tatsuma, Adv. Mater. Interfaces, 1, 1400066 (2014). Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, and A. Fujishima, Nat. Mater., 2, 29 (2003). E. Kazuma, N. Sakai, and T. Tatsuma, Chem. Commun., 47, 5777 (2011). I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012). K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016). Figure 1

Plasmon-induced charge separation (PICS) occurs at the interface between plasmonic nanostructures of Au, Ag, or Cu and a semiconductor (e.g., TiO2).1-3 Carrier transfer from the nanostructure to the semiconductor due to external photoelectric effects (including hot carrier injection) or interfacial electron transition is responsible for PICS.4 We reported PICS for the first time more than 10 years ago1,2 and studied its mechanisms4,5 and applications.1,3,6,7 In particular, we have reported effects of localized electric field on PICS. In the case of PICS-based oxidation of Ag nanoparticles, anodic reaction (i.e., oxidation of Ag to Ag+) occurs preferentially at the sites where optical near field is localized.8-10 This may be explained in terms of ejection of energetic holes from the nanoparticles as Ag+ ions.10 1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005). 2. Y. Tian and T. Tatsuma, Chem. Commun., 2004, 1810. 3. T. Tatsuma, Bull. Chem. Soc. Jpn., 86, 1 (2013) [account]. 4. E. Kazuma and T. Tatsuma, Adv. Mater. Interfaces, 1, 1400066 (2014). 5. H. Nishi and T. Tatsuma, Angew. Chem. Int. Ed., 55, 10771 (2016). 6. Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, and A. Fujishima, Nat. Mater., 2, 29 (2003). 7. Y. Takahashi and T. Tatsuma, Appl. Phys. Lett., 99, 182110 (2011). 8. E. Kazuma, N. Sakai, and T. Tatsuma, Chem. Commun., 47, 5777 (2011). 9. I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012). 10. K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).

The equimolar mixture of lithium bis(trifluoromethylsulfonyl)amide (LiTFSA)-tetraglyme (G4) has been known as a solvate ionic liquid consisting of [Li(G4)]+ and TFSA–. This solvate ionic liquid contains lithium ions in high concentration (ca. 3 mol dm–3) and has negligible vapor pressure at ambient temperature. It has been reported that the solvate ionic liquid is compatible with sulfur cathode because of the low solubility of lithium polysulfides [1]. To achieve the high energy density of the rechargeable Li-S batteries, it is required to investigate anode materials having high specific capacity such as a lithium anode. In this study, the initial stage of deposition of lithium was investigated in the solvate ionic liquids with different compositions using electrochemical quartz crystal microbalance (EQCM) and optical microscope. LiTFSA-G4 solvate ionic liquids were prepared by mixing LiTFSA and G4 at different molar ratios of LiTFSA (X LiTFSA) in an Ar filled glove box. The potentials of Li(I)|Li were evaluated using a Ag|Ag(I) reference electrode, which consisted of a silver wire immersed in 50.0-50.0 mol% LiTFSA-G4 containing 0.1 mol dm–3 AgCF3SO3. EQCM measurement was performed with an airtight three-electrode cell. A Cu coated quartz crystal electrode was used as a working electrode. Lithium was used as a reference and counter electrode. [Li(G4)]+ is considered a major lithium species in LiTFSA-G4 solvate ionic liquid at X LiTFSA = 50 mol%. On the other hand, both [Li(G4)]+ and [Li(TFSA)2]– are expected to exist in LiTFSA-G4 solvate ionic liquid at X LiTFSA > 50 mol%. It was found that the potential of Li(I)|Li in the LiTFSA-G4 solvate ionic liquid at X LiTFSA > 50 mol% was given by an equilibrium, [Li(TFSA)2]– + e– = Li + 2TFSA–, indicating the active lithium species is [Li(TFSA)2]– rather than [Li(G4)]+. Li was deposited at a current density of –0.01 mA cm–2. The electric charge for deposition was –0.05 C cm–2. In the case of 54.5-45.5 mol% LiTFSA-G4 solvate ionic liquid, Li was deposited sparsely on the Cu electrode surface and grew as a whisker-like shape. On the other hand, whisker-like Li deposit was not observed in 50.0-50.0 mol% LiTFSA-G4 solvate ionic liquid where Li nuclei were uniformly generated on the electrode surface. These results suggest that the nucleation and crystal growth of Li are affected by the composition of the solvate ionic liquids, resulting in the morphology change of Li deposits. Acknowledgment This study was supported by the Advanced Low Carbon Technology Research and Development of Program (ALCA) of the Japan Science and Technology Agency (JST). Reference [1] K. Dokko et al., J. Electrochem. Soc., 160, A1304 (2013).

Introduction Metal nanoparticles, such as gold and silver nanoparticles (AuNPs and AgNPs), have attracted much attention because they can generate strong enhanced electromagnetic fields in nanospaces around the metal nanoparticle surfaces by coupling with incident light in the wavelength region of visible to near-IR on the basis of localized surface plasmon resonance (LSPR). Hence, they can be applied to enhancement of both absorption and emission processes of the light-absorbing molecules and/or semiconductors placed in the nanospaces. Meanwhile, noble metal nanoparticles composited with n-type semiconductors, such as TiO2 and ZnO, exhibit plasmon induced charge separation (PICS).[1,2] When the light with resonant wavelength region irradiates the composition, the electrons of the metal nanoparticle are transferred to the n-type semiconductor resulting in reductive and oxidative reactions on the surfaces of the n-type semiconductor and the metal nanoparticles, respectively. This phenomenon has been utilized to unique applications, such as visible light responsive photocatalysts, photovoltaic cells, and sensing devices. In this study, we employed AuNP-TiO2 system so as to apply PICS as a site-selective nanoscale-polymerization method. Experimental A smooth TiO2 layer was obtained on a heat resistance glass plate by the spray pyrolysis technique, in which a 2-propanol solution containing 0.3 M titanium diisopropoxide bis(acetylacetonate).[3,4] Then, AuNPs were photocatalytically deposited onto the TiO2 substrate from a water/ethanol (v/v=3:2) solution containing 0.2 mM HAuCl4 for 15 min under UV light. Visible-light irradiation was carried out equipped with a UV sharp cut filter. Monochromatic light from a Xe lamp was also employed for action spectra measurements. (Fig. 1) Results and discussion First, we irradiated visible light to the AuNP-TiO2 substrate in an aqueous solution containing 10 mM pyrrole so that pyrrole was polymerized by anodic potential based on PICS at the interface region between AuNPs and TiO2. From UV-vis spectra before and after the irradiation, the absorbance of the substrate increased and the plasmon peak on the basis of AuNPs showed red-shift. X-ray photoelectron spectroscopic (XPS), Raman spectroscopic and scanning electron microscopic (SEM) measurements revealed that these changes of the spectra were caused by site-selective nanoscale-deposition of polypyrrole on the surfaces of AuNPs. An action spectrum of the increment of extinction intensity at 420 nm (π-π* of pyrrole) was well correlated with the extinction spectrum of AuNPs. These results verified that the polymerization should be proceeded via PICS.[5] We found that the polymerization method can also be applied to other monomers, such as phenol, 2,2’-bithiophene, and 3,4-ethylenedioxythiophene (EDOT). References [1] Y. Tian, T. Tatsuma, J. Am. Chem. Soc., 2005, 127, 7632. [2] T. Tatsuma, Bull. Chem. Soc. Jpn., 2013, 86, 1. [3] Y. Takahashi, T. Tatsuma, Appl. Phys. Lett., 2011, 99, 182110. [4] T. Kawawaki, Y. Takahashi, T. Tatsuma, Nanoscale, 2011, 3, 2865. [5] Y. Takahashi, Y. Furukawa, T. Ishida, S. Yamada, Nanoscale, in press. Figure 1

The equimolar mixture of lithium bis(trifluoromethylsulfonyl)amide (Li[N(CF3SO2)2] or LiTFSA) and triglyme (G3) or tetraglyme (G4) has been known to give a solvate ionic liquid, which is composed of Li+ solvated by glyme and TFSA–. Since Li+is strongly coordinated by the glyme molecule, the vapor pressure at ambient temperature is negligible. In addition, the high concentration of Li(I) species in the solvate ionic liquids is considered favorable for the electrolytes of rechargeable lithium batteries. Furthermore, the solvate ionic liquids have been expected to be applied for the electrolytes of rechargeable sulfur batteries because of the low solubility of lithium polysulfides [1]. In order to make the best use of the high specific capacity of the sulfur cathode, it is favorable to employ lithium or silicon as the anode material. In the present study, the charge-discharge characteristics of lithium and silicon anodes were investigated in LiTFSA-glyme (G3 or G4) solvate ionic liquids containing excess LiTFSA. Galvanostatic charge-discharge experiments were conducted with 2032 coin-type cells. Copper and silicon thin film prepared by RF magnetron sputtering on a copper foil were used as a working electrode. Lithium was used as a counter electrode. A polypropylene-based porous membrane was used as a separator. The solvate ionic liquids prepared by mixing LiTFSA and glyme (G3 or G4) at the molar ratios of 1 : 1 and 1.2 : 1 were used as the electrolytes, which are denoted by 50.0-50.0 and 54.5-45.5 mol% LiTFSA-glyme, respectively. The coulombic efficiency for deposition and dissolution of lithium on the copper substrate was examined at ±0.1 mA cm–2 with the cut-off voltage of 2 V. The electric charge for deposition was 0.2 C cm–2. The coulombic efficiency in both 50.0-50.0 and 54.5-45.5 mol% LiTFSA-glyme increased within the first ten cycles and exceeded more than 90% until 50 cycles. The efficiency in 54.5-45.5 mol% LiTFSA-glyme was greater than that in 50.0-50.0 mol% one, suggesting addition of excess LiTFSA to the solvate ionic liquids improves the coulombic efficiency. The coulombic efficiency for alloying and dealloying of silicon and lithium was also examined in the same electrolytes at ±0.05 mA cm–2 within the voltage range from 0.01 to 2 V. Reversible cycling was possible with the specific discharge capacity of more than 2400 mAh g–1-Si in both 50.0-50.0 and 54.5-45.5 mol% LiTFSA-G4. The coulombic efficiency of more than 99% was achieved with the silicon thin film anode within 30 cycles while significant capacity fading was observed within a few cycles in LiTFSA-G3 solution at the molar ratio of 1 : 4. High coulombic efficiency of lithium and silicon anodes in the solvate ionic liquids containing excess LiTFSA may be due to the low activity of free glymes in the electrolyte. Addition of LiTFSA to 50.0-50.0 mol% LiTFSA-glyme is considered to introduce a Li+ species, [Li(TFSA)2]–, which is known to form in other TFSA–-based ionic liquids, and decrease the activity (or life-time) of free glyme, which may react with lithium and lithiated silicon and cause capacity fading. References 1. K. Dokko, N. Tachikawa, K. Yamauchi, M. Tsuchiya, A. Yamazaki, E. Takashima, J.-W. Park, K. Ueno, S. Seki, N. Serizawa, and M. Watanabe, J. Electrochem. Soc., 160(8), A1304 (2013).